The present invention relates to a bearing ball cage of a ring shaped configuration, in which a pocket for accommodating a ball for a ball bearing assembly is defined at a plurality of locations in a direction circumferentially thereof and each of those pockets has an inner surface so shaped as to represent a concaved surface shape, and also to a method of manufacturing such bearing ball cage.
The present invention relates to a bearing ball cage of a ring shaped configuration, in which a pocket for accommodating a ball for a ball bearing assembly is defined at a plurality of locations in a direction circumferentially thereof and each of those pockets has an inner surface so shaped as to represent a concaved surface shape, and also to a method of manufacturing such bearing ball cage.
Various rotary devices, particularly sealed ball bearing assemblies that are used in automobile accessories are required to have a high thermostability, a resistance to high speed or high withstand speed, a resistance to muddy water, a resistance to dust, a resistance to grease leakage, a long lifetime and a low torque, and a space delimited between a bearing inner ring and a bearing outer ring in each of those bearing assemblies has its opposite ends provided with respective contact seals for the purpose of the resistance to muddy water and the resistance to dust.
In the sealed ball bearing assembly of the structure referred to above, in the event that the bearing temperature increased while grease is present in a sealing lip segment of one of the contact seals, the pressure inside the ball bearing assembly increases as a result of expansion of air within the ball bearing assembly and, accordingly, the sealing lip segment of the contact seal opens with the grease and/or air inside the ball bearing assembly consequently leaking to the outside of the ball bearing assembly due to the difference in pressure from the outside (which phenomenon is hereinafter referred to as a “breathing”). (See the Patent Document 1 listed below.)
To avoid the above discussed breathing, the provision has been suggested of a ventilating cutout in a portion of the sealing lip segment. (See the Patent Document 1 listed below.) It has, however, been found that once grease deposits on the cutout, leakage of the grease will occur as is the case with the ball bearing assembly discussed hereinabove. (See the Patent Document 2 listed below.)
Although it may be contemplated that without using the above discussed ventilating cutout, in a ball bearing assembly of, for example, an inner ring rotating type, an urging pressure (hereinafter referred to as a “tensioning force”) for urging the sealing lip segment against a seal groove defined in an inner ring outer diametric surface, to which the sealing lip segment of the contact seal is urged, is strengthened to enhance prevention of the breathing, this approach merely results in increase of the torque and, in the event of a considerable temperature increase enough to result in an internal pressure higher than the tensioning force, there is no way of preventing the grease leakage. Also, in the event that the bearing temperature decreases, since the internal pressure lowers as a result of contraction of air inside the ball bearing assembly, an absorbing phenomenon of a foremost end of the sealing lip segment occurs, thus causing further increase of the torque. (See, for example, the Patent Document 3 listed below.)
Because of the foregoing reasons, even if any of the above discussed various structures is employed for the contact seal, it is difficult to avoid leakage of the grease once the grease deposits on the inner ring seal groove.
As a sealed ball bearing assembly, other than those discussed hereinabove, the type has been suggested, in which a cage is so sophisticatedly configured to avoid the grease leakage. (See, for example, the Patent Documents 4 and 5 listed below.) The cage disclosed in the Patent Document 4 is the type, in which in an inner surface of each of pockets, instead of an outer diametric side end portion being constricted to a diameter smaller than or equal to that of each ball, an inner diametric side portion is so designed as to represent a cylindrical surface of a diameter larger than that ball diameter. The cage disclosed in the Patent Document 5 is the type, in which a ball confronting surface of each pocket is formed with at least four projections so that each ball can be retained therein solely in contact with the projections.
[Patent Document 1]JP Laid-open Patent Publication No. 2000-257640
[Patent Document 2]JP Laid-open Patent Publication No. 2005-308117
[Patent Document 3]JP Laid-open Patent Publication No. 2005-069404
[Patent Document 4]JP Laid-open Patent Publication No. 2001-116051
[Patent Document 5]JP Laid-open Patent Publication No. 2003-239984
It has however been found that in the ball bearing assemblies disclosed respectively in the Patent Documents 4 and 5, each of the balls is retained by points or small surface areas and, therefore, the surface pressure tends to be high. For this reason, if the cage is made of a resinous material, it tends to be frictionally worn out quickly. Also, no application thereof can be made to a cage of a kind made by the use of the iron plate blanking technique. That is because, if a part of the shape is applied to the cage of the kind made by the use of the iron plate blanking technique, in the inner diametric side of the cage, the distance to the sealing lip segment will be too small, thus permitting the grease deposited on the cage to urge the sealing lip segment, accompanied by occurrence of the grease leakage. Also, it may be suspected that the torque may increase due to a shearing of the grease.
As discussed hereinabove, as a method to avoid the grease leakage, there are a tensioning force of the sealing lip segment, the shape of the sealing lip segment, the cutout and so on, but if due to rotation grease is present in an inner ring shoulder and/or seal groove, the possibility of occurrence of the grease leakage will become high. In particular, in the case of an outer ring rotation, since no centrifugal force acts on the inner ring, the grease once deposited in the inner ring seal groove will remain deposited therein. When while in this condition the temperature of the ball bearing assembly increases, the grease leakage will occur as a result of the breathing. Also, in the countermeasure by changing the shape of the cage, there are problems associated with the strength and frictional wear in the case of the resinous cage and, in the case of the cage made from a blanked iron plate, difficulty will be encountered in manufacturing the same.
FIGS. 23A to 23C illustrate a process of movement of the grease into the inner ring seal groove. As shown in FIG. 23A, when the surface of one of the balls 44 enters the corresponding pocket 51 on an inner diametric side of the cage 45, grease G sticking to such surface is scraped off to deposit, and then remain deposited, on an inner diametric portion of the cage 45 (a grease puddle G1). When the amount of grease so puddle becomes larger as a grease puddle (shown by the hatching) G2 shown in FIG. 23B, it comes to deposit in a shoulder of the inner ring 42. When puddle of the grease puddle G2 forms, it will collide against the preceding grease puddle G1 and then ride slantwise over it (a grease puddle G3) as shown in FIG. 23C and subsequently deposit onto the seal groove 49 incident to upwelling towards a central portion inside the respective pocket 51. Because of the deposit of the grease in the seal groove 49 in this way, the above discussed problems and inconveniences occur.
Also, the previously described iron made cage tends to involve generation of friction induced swarf of iron in sliding contact with a steel ball during the operation, which eventually leads to reduction in lifetime of the ball bearing assembly. In the event that a crown shaped, resin made cage is used, the lifetime will prolong, but deformation occurs during the high-speed operation under the influence of a centrifugal force and, therefore, the cage will contact an outer ring inner diametric surface and/or constrains the steel ball.